DECEMBER, 1971 50c - Desert Magazine of the Southwest

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Yuma; above the Morelos dam and probably—but
not positively—from below
the Imperial dam.
After seeing this vast area below the
border, both from the ground and the
air, we were able to arrive at a theory as
to how and why the river shifted its
course sometime in the late 1700s In
those early days the gulf tapered to the
north, so that as the tides progressed up
its 750 mile length from south to north
they became higher and advanced more
rapidly as the surface area narrowed.
Tidal bores in excess of 20 feet are a
matter of record. These great bores were
dissipated when they reached the north
of the gulf and spread out over the
tidal flats where the desert and dunes
now lay, and at ebb tide would deposit
their vast burdens of sand. Surface temperatures
in the area have been reported
at 180 degrees in the summer months.
The blistering sun dried out the top
sands in a matter of minutes after the
tide receded, and they would be drifted
by the prevailing westerly winds forming
the great dunes as they now exist.
Where the force of the incoming tides
met the current of the river huge sandbars
were formed and were enlarged by the
debris and silt carried by the river.
Francisco de Ulloa, one of the earliest
explorers to sail to the mouth of the Colorado
in 1647 reported, "A recent downpour
to the north had put the river in
flood so that down the estuary came
floating great clots of grass-matted soil,
trunks of trees and other light debris.
Sometimes it was the color of lime—the
color of a river in flood, then yellow,
then dark brown, and again the color of
chocolate or nearly black from the volcanic
contents of the soil."
With the formation of these bars of
silt and sand, the channels of the delta
were choked and eventually dammed.
The river became deeper and its waters
backed up to the confluence with the
Gila River, or farther up both rivers, and
spread across the tidal flats surrounding
the delta. Finally a trickle overflowed
the once-high west bank of the Colorado.
While the bank washed away the trickle
became a flow, and the flow a torrent
as the river rushed out into the lower
lands to the southwest. Several hundred
square miles were flooded before the
rampaging river once again settled down
in its ancient stream bed to the west.
The water flowing over the west bank
cut deep to a ledge of bedrock where it
could go no deeper. This, however, was
not as deep as the bed the river had followed
for several centuries. A greatly
reduced flow continued as it had before.
With the diminished volume of water
going down the channel toward Adair
Bay the river and the flood waters in
the delta gradually stagnated and could
no longer carry away the blowing sands
as they settled. Over a period of time
the channels became filled to the top of
their banks. Capillary action carried the
moisture upward, dampening the sands
as fast as the winds deposited them, first
forming ridges and then dunes that continued
to grow into great sand hills. As
the moisture reached the top of the sand
it evaporated where the arid desert air
reached it-
Waters gradually drained from the
flood plains of the delta, joining the flow
still coming down the old channels. Bit
by bit the water built up pressure when
the capillary action and evaporation
could no longer handle it. The flow became
more concentrated and its velocity
increased as seepage broke through under
the old barriers and soon became a free
flowing underground river into Adair
Bay.
The last inhabitants who might have
seen this all take place were the Arenero
Indians. Most of them left while the
waters were disappearing; the last of
them were run out or killed by a Mexican
posse nearly a century ago—they had
been responsible or were so accused, for
more than 50 murders and robberies
along the Camino del Diablo. They left
no written records and their legends died
with them. Consequently the "how" and
"why" the river changed is course is a
matter of conjecture based on existing
evidence, with a few educated guesses
to fit the pieces together.
The amount of irrigation water being
lost before it reaches the Alamo Canal
and possibly, but not probably, from the
All American Canal is also a matter of
conjecture until the comparative flows
can be measured.
In any event, if you're boating down
the lower Colorado take the right hand
branch—the other has a very low ceiling.
•
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TROUT, BASS AND CATFISH
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